Rationale for anti-CD200 immunotherapy in B-CLL and other hematologic malignancies: new concepts in blocking immune suppression.

Immune evasion in cancer is increasingly recognized as a contributing factor in the failure of a natural host antitumor immune response as well as in the failure of cancer vaccine trials. Immune evasion may be the result of a number of factors, including expansion of regulatory T cells, production of immunosuppressive cytokines, downregulation of HLA class I and tumor-associated antigens and upregulation of immunosuppressive molecules on the surface of tumor cells. CD200, a cell surface ligand that plays a role in regulating the immune system, has been shown to be upregulated on the surface of some hematologic and solid tumor malignancies. This review characterizes the role of CD200 in immune suppression, and describes strategies to target this molecule in the oncology setting, thus directly modulating immune regulation and potentially altering tolerance to tumor antigens.